The widespread weed bastard cabbage (Rapistrum rugosum) is one of a number of species with similar yellow, mustard-like flowers. It is recognised by its small fruits, which occur along the stems as small sheres with a narrow beak. A native of the Eastern Mediterranean, it is extremely invasive. It can rapidly spread to fill a field creating a monoculture which shades out other more delicate species. It has been introduced into N. America, where it has begun to cause serious problems, particularly in Texas.